1. Field of the Invention
This invention relates to portable power working machines such as backpack blower apparatus and, more particularly, is concerned with a technique for reducing noise from a centrifugal blower as used in a portable power working machine.
2. Related Background Art
In portable power working machines using centrifugal blowers, conventionally various means have been suggested for reducing noise caused from the centrifugal blowers. For example, U.S. Pat. No. 5,195,208 discloses a backpack blower apparatus which is covered with a sound-shielding sheet at the left and right sides and rear portion thereof. U.S. Pat. No. 5,857,439 discloses a backpack power working machine having a sound-absorbing panel provided in a manner closing the gaps in the left and right between the backpack frame and the centrifugal blower.
In the typical backpack power working machine, an intake port of the centrifugal blower is directed toward the backpack frame, thus requiring air to be taken through the gap between the centrifugal blower and the backpack frame. Consequently, in the conventional power working machine having a sound-shielding sheet or sound-absorbing panel as above, the upper gap is widely opened between the backpack frame and the centrifugal blower.
However, where the upper gap is widely opened between the backpack frame and the centrifugal blower, comparatively large foreign matter, such as fallen leaves, enters through the gap and is possibly caught by a net provided in the intake port of the blower. In such a case, the foreign matter must be removed away. However, because the gap is narrow between the backpack frame and the centrifugal blower, there is a problem that time and labor is required for removing the same.
In order to solve the above problem, a portable power working machine according to the present invention comprising: a frame having a horizontal portion and an upright portion rising from one end of the horizontal portion; a centrifugal blower having an intake port opposed to the upright portion and rested and fixed on the horizontal portion with spacing to the upright portion; a cover having an upper portion spanned between an upper portion of the upright portion and the centrifugal blower and side portions extending from respective ends of the upper portion to the horizontal portion and spanned between side portions of the upright portion and the centrifugal blower; a plurality of through-holes being formed in the upper portion of the cover to communicate an interior space defined by the frame, the centrifugal blower and the cover with an exterior space at an outside of the interior space, the through-hole having a dimension to block a foreign matter in a size greater than a predetermined value from passing through.
With this arrangement, the noise propagated laterally through a gap between the frame upright portion and the centrifugal blower is shielded by the side portion of the cover. Also, although the air to the centrifugal blower is taken through the through-holes in the upper portion, the through-holes are small in size and hence foreign matter, such as large fallen leaves, does not reach to the intake port of the centrifugal blower.
The portable power working machine does not only includes a backpack blower apparatus, but also a backpack spray apparatus, a shoulder blower apparatus and a shoulder spray apparatus.
The cover preferably comprises a sheet member having a first portion structuring the upper portion and second portions extending from respective ends of the first portion to the frame horizontal portion and attached to a side surface of the frame, and a sound-absorbing member fixed on a surface of the second portion of the sheet member on a side of the interior space. The presence of the sound-absorbing member improves the effect of suppressing noise.
It is preferred to fix a sound-absorbing member on the first portion of the sheet member, i.e., the surface in the upper portion of the cover on the side of the internal space. This sound-absorbing member further improves the effect of suppressing noise. Of course, this sound-absorbing member has to be formed with through-holes communicating with the through-holes of the sheet member.
In the case that the sound-absorbing member is made of an elastically deformable material and put in close contact, without gaps, with the side surface of the centrifugal blower, sound-insulating and sound-absorbing properties are improved.
If the sheet member is made in an integral structure, merely attaching the sheet member to the frame completes attaching the sound-absorbing member.
Furthermore, the cover itself may be constructed by a rigid sound-absorbing member only. It is possible to contemplate as a rigid sound-absorbing member a plate having a honeycomb core member and surface plates bonded on opposite surfaces of the honeycomb core member. In this case, as for a honeycomb sandwich plate portion corresponding to the cover upper portion, the interior space and the exterior space are made in communication by removing the surface plate.
Another sound-absorbing member may be fixed on a surface of the side portion comprising a honeycomb sandwich plate on the side of the interior space.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.